Sheet processing apparatus

ABSTRACT

A sheet processing apparatus includes a processing tray; a conveyance roller for conveying a sheet towards a downstream side in a sheet conveyance direction; a pinch roller for moving between a first position away from the conveyance roller and a second position close to the conveyance roller, and to sandwich the sheet with the conveyance roller at the second position when the sheet is conveyed by the conveyance roller. The apparatus further includes an extruding member for extruding an upstream end of the sheet from the upstream side towards the downstream side to convey the sheet placed on the processing tray. The apparatus additionally includes a controller for conveying the sheet with the extruding member after the sheet is conveyed by the pinch roller and the conveyance roller when the sheet on the processing tray is conveyed to the downstream side in the sheet conveyance direction.

CROSS -REFERENCE to RELATED APPLICATION

This application, is based upon and claims the benefit of priority fromJapanese Patent Application No. 2017-170374, filed Sep. 5, 2017, theentire contents of which are incorporated herein by reference.

FIELD

Embodiments described herein relate generally to a sheet processingapparatus.

BACKGROUND

A sheet processing apparatus executes a post-processing such as sortingand stapling on a sheet-like image receiving medium (hereinafter,referred to as a “sheet”) conveyed from an image forming apparatus. Thesheet, processing apparatus includes a standby section, a processingsection, and a discharge section. The standby section temporarilyretains the sheet. The standby section sends the retained sheet to theprocessing section at a prescribed timing. The processing sectionexecutes the post processing by aligning the sheet received from thestandby section. The processing section discharges the sheet subjectedto the post-processing to the discharge section.

For example, when the sheet is discharged to the discharge section, theprocessing section extrudes an edge of the sheet on an upstream side ina conveyance direction towards a downstream side in the conveyancedirection with an extruding member. However, there is a possibility thatthe sheet extruded by the extruding member bends.

For example, when the sheet is discharged to the discharge section, theprocessing section sandwiches the sheet between a pinch roller and aconveyance roller to convey the sheet by the rotation of the pinchroller and the conveyance roller. However, there is a possibility thatthe pinch roller and the conveying roller could slide against the sheet.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram schematically exemplifying the overall configurationof an image forming system according to at least one embodiment;

FIG. 2 is a block diagram exemplifying functional components of an imageforming apparatus and a sheet processing apparatus according to at leastone embodiment;

FIG. 3 is a side view schematically exemplifying the configuration of asheet processing apparatus according to at least one embodiment;

FIG. 4 is a first flowchart for depicting a flow of a third dischargeprocess in the sheet processing apparatus according to at least oneembodiment;

FIG. 5 is a second flowchart for depicting the flow of the thirddischarge process in the sheet processing apparatus according to atleast one embodiment;

Fig. 6 is a side view illustrating a first operation state in the thirddischarge process of the sheet processing apparatus according to atleast one embodiment;

FIG. 7 is a side view illustrating a second operation state in the thirddischarge process of the sheet processing apparatus according to atleast one embodiment;

FIG. 8 is a side view illustrating a third operation state in the thirddischarge process of the sheet processing apparatus according to atleast one embodiment;

FIG. 9 is a side view illustrating a fourth operation state in the thirddischarge process of the sheet processing apparatus according to atleast one embodiment;

FIG. 10 is a side view illustrating a fifth operation state in the thirddischarge process of the sheet processing apparatus according to atleast one embodiment;

FIG. 11 is a side view illustrating a sixth operation state in the thirddischarge process of the sheet processing apparatus according to atleast one embodiment;

FIG. 12 is a side view illustrating a seventh operation state in thethird discharge process of the sheet processing apparatus according toat least one embodiment; and

FIG. 13 is a side view illustrating an eighth operation state in thethird discharge process of the sheet processing apparatus according toat least one embodiment.

DETAILED DESCRIPTION

In accordance with at least one embodiment, a sheet processing apparatuscomprises a processing tray; a conveyance roller, arranged on adownstream side in a sheet conveyance direction with respect to theprocessing tray, configured to convey a sheet towards the downstreamside in the sheet conveyance direction; a pinch roller configured tomove between a standby position away from the conveyance roller and arotational position close to the conveyance roller, and to sandwich thesheet with the conveyance roller at the rotational position when thesheet is conveyed by the conveyance roller; an extruding memberconfigured to extrude an upstream end of the sheet in the sheetconveyance direction from the upstream side towards the downstream sidein the sheet conveyance direction to convey the sheet placed on theprocessing tray; and a controller configured to control the conveyanceroller, the pinch roller and the extruding member in such a manner as tomove the pinch roller to the rotational position if the sheet placed onthe processing tray is conveyed to the downstream side in the sheetconveyance direction, move the pinch roller to the standby positionafter the sheet is conveyed by the pinch roller and the conveyanceroller, and then convey the sheet with the extruding member.

Hereinafter, a sheet processing apparatus according to an embodiment isdescribed with reference to the accompanying drawings.

In the following figures, the same component is denoted with the samereference numeral.

FIG. 1 is a diagram schematically exemplifying the overall configurationof an image forming system 1 according to the embodiment. FIG. 2 is ablock diagram exemplifying the functional components of an image formingapparatus 2 and a sheet processing apparatus 3 according to theembodiment.

The image forming system 1 is provided with the image forming apparatus2 and the sheet processing apparatus 3. The image forming apparatus 2forms an image on a sheet-like medium (hereinafter, collectivelyreferred to as a “sheet S”) such as a paper. The sheet processingapparatus 3 executes a post-processing on the sheet S discharged fromthe image forming apparatus 2.

The image forming apparatus 2 includes a control panel 11, a scannersection (a scanner) 12, a printer section (a printer) 13, a sheet feedsection (a feeder) 14, a sheet discharge section (a discharger) 15 andan image forming controller 16.

The control panel 11 includes an operation section, a display sectionand a panel controller. The operation section receives an operation by auser. For example, the operation section includes various keys and atouch panel. The display section displays various information. The panelcontroller controls reception of an operation by the user on theoperation section and display on the display section. The panelcontroller includes a control circuit having a CPU (Central ProcessingUnit), a ROM (Read Only Memory), and a RAM (Random Access Memory). Thecontrol circuit may carry out operations according to program-executableinstructions stored in a non-transitory memory.

For example, the control panel 11 receives an input relating to thesheet S such as a size (sheet size) of the sheet S and the type of thesheet S. The sheet size includes a regular size and an irregular size.The type of the sheet S includes a paper quality, a quantity, athickness, and the like.

For example, the control panel 11 receives an input relating to the typeof the post-processing carried out on the sheet S. The control panel 11receives a selection of any one of a plurality of different processingmodes. The plurality of different processing modes includes a sortingmode, a stapling mode and a non-sorting mode. The sorting mode refers toa processing mode in which a sorting process is executed. The staplingmode refers to a processing mode in which a binding process (staplingprocess) by a staple is executed. The non-sorting mode refers to aprocessing mode in which the execution of the sorting process and thestapling process is prohibited. For example, in a case of receiving theselection of the stapling mode, the control panel 11 receives an inputrelating to the number of sheets S (the number of stapled sheets)forming a shoot bundle SS.

For example, at the time of receiving selection of the non-sorting mode,the control panel 11 receives selection of any one of a plurality ofdischarge destinations for the sheet S. The plurality of dischargedestinations includes a fixed tray 23 a and a movable tray 23 bdescribed later.

The image forming apparatus 2 sends the information relating to thesheet S and the information relating to the type of the post-processingreceived by the control panel 11 to the sheet processing apparatus 3.

The scanner section 12 includes a reading section and a scannercontroller. The reading section reads image information which is a copyobject as intensity of light. The scanner controller controls reading ofthe image information by the reading section. The scanner controllerincludes a control circuit having a CPU, a ROM, and a RAM. The scannersection 12 sends the read image information to the printer section 13.

The printer section 13 forms an output image (hereinafter, referred toas a “toner image”) with a developer such as a toner based on the imageinformation received from the scanner section 12 or an external device.The printer section 13 transfers the toner image onto the surface of thesheet S. The printer section 13 applies heat and pressure to the tonerimage on the surface of the sheet S to fix the toner image on the sheetS. The printer section 13 sends the sheet S on which the toner image isfixed to the sheet discharge section 15. The printer section 13 includesa printer controller. The printer controller includes a control circuithaving a CPU, a ROM, and a RAM. The printer controller controls theprinting of the image on the sheet S by the printer section 13.

The sheet feed section 14 supplies the sheets S one by one to theprinter section 13 in accordance with a timing at which the printersection 13 forms the toner image. For example, the sheet feed section 14includes a plurality of the sheet feed cassettes. Each of the sheet feedcassettes accommodates a sheet S of a predetermined size and type inadvance. Each of the sheet feed cassettes has a pickup roller. Eachpickup roller picks up the sheets S one by one from each of the sheetfeed cassettes. Each pickup roller sands the sheet S taken out from eachof the sheet feed cassettes to the printer section 13.

The sheet discharge section 15 conveys the sheet S received from theprinter section 13 to the sheet processing apparatus 3.

The image forming controller 16 controls the whole operations of theimage forming apparatus 2. The image forming controller 16 controls thecontrol panel 11, the scanner section 12, the printer section 13, thesheet feed section 14 and the sheet discharge section 15. The imageforming controller 16 includes, for example, a CPU, a ROM and a RAM.

The sheet processing apparatus 3 is arranged adjacently to the imageforming apparatus 2. The sheet processing apparatus 3 executes thepost-processing designated via the control panel 11 on the sheet Sconveyed from the image forming apparatus 2. For example, thepost-processing is the sorting process, the stapling process, or thelike.

The sheet processing apparatus 3 includes a standby section 21, aprocessing section 22, a discharge section 23, a conveyance section 24,a post-processing controller 25, a bundle claw driving mechanism 61, anda pinch roller driving mechanism 71.

The standby section 21 temporarily retains the sheet S received from theimage forming apparatus 2. For example, a plurality of succeeding sheetsS stands by on the standby section 21 while the post-processing isexecuted on the former sheet S by the processing section 22. The standbysection 21 is arranged above the processing section 22 in a verticaldirection. A plurality of sheets S overlaps in a thickness direction andstands by on the standby section 21. If the processing section 22 is ina state capable of receiving the sheet S, the standby section 21 dropsthe sheet S that is being retained towards the processing section 22.

The processing section 22 carries out the post-processing on the sheet Sreceived from the standby section 21. For example, the processingsection 22 carries out the sorting process for gathering a plurality ofsheets S and then aligning them. For example, the processing section 22carries out the binding process (stapling process) with a staple on thesheet bundle SS formed by gathering a plurality of sheets S. Theprocessing section 22 discharges the sheet S on which thepost-processing is carried out to the discharge section 23.

The discharge section 23 supports the sheet S received from the standbysection 21 and the processing section 22. The discharge section 23includes the fixed tray 23 a and the movable tray 23 b. For example, thefixed tray 23 a is arranged at the upper part of the sheet processingapparatus 3. For example, the movable tray 23 b is arranged on the sideof the sheet processing apparatus 3. The movable tray 23 b moves in anupper and lower direction along the side of the sheet processingapparatus 3. For example, the upper and lower direction is the verticaldirection. The fixed tray 23 a and the movable tray 23 b support thesheet S received from the standby section 21 and the processing section22.

The conveyance section 24 includes a conveyance path 31, an inlet rollermechanism 32, and an outlet roller mechanism 33.

The conveyance path 31 is provided inside the sheet processing apparatus3. The conveyance path 31 guides the sheet S received from the imageforming apparatus 2 to the standby section 21, the processing section22, or the discharge section 23. The conveyance path 31 includes a firstconveyance path 31 a, a second conveyance path 31 b and a thirdconveyance path 31 c which bifurcate from the first conveyance path 31a. The first conveyance path 31 a guides the sheet S to the standbysection 21. The second conveyance path 31 b guides the sheet S to thefixed tray 23 a of the discharge section 23. The third conveyance path31 c guides the sheet S to the processing section 22.

The inlet roller mechanism 32 is arranged between the upstream end ofthe conveyance path 31 in the sheet conveyance direction and the sheetdischarge section 15 of the image forming apparatus 2. The inlet rollermechanism 32 sends the sheet S received from the image forming apparatus2 to the conveyance path 31.

The outlet roller mechanism 33 is arranged between the downstream end ofthe first conveyance path 31 a in the sheet conveyance direction and thestandby section 21. The outlet roller mechanism 33 sends the sheet Sreceived from the first conveyance path 31 a to the standby section 21.

The post-processing controller 25 controls the whole operations of thesheet processing apparatus 3. The post-processing controller 25 controlsthe standby section 21, the processing section 22, the discharge section23, the conveyance section 24, the bundle claw driving mechanism 61, andthe pinch roller driving mechanism 71. The post-processing controller 25includes a control circuit having a CPU, a ROM, and a RAM.

Details of the structure of the sheet processing apparatus 3 aredescribed below.

FIG. 3 is a side view schematically exemplifying the configuration ofthe sheet processing apparatus 3 according to the embodiment.

The conveyance section 24 includes the conveyance path 31 where a sheetsupply port 31 d and a sheet discharge port 31 e are formed. The sheetsupply port 31 d is formed to face the sheet discharge section 15 of theimage forming apparatus 2 at the upstream end of the conveyance path 31in the sheet conveyance direction. The sheet S discharged from the imageforming apparatus 2 is sent to the conveyance path 31 through the sheetsupply port 31 d. The sheet discharge port 31 e is formed to face thestandby section 21 at the downstream end of the first conveyance path 31a in the sheet conveyance direction. The sheet S passing through thefirst conveyance path 31 a is sent to the standby section 21 through thesheet discharge port 31 e.

The first conveyance path 31 a guides the sheet S to the standby section21 through the sheet supply port 31 d if the sorting mode or thestapling mode is selected.

The second conveyance path 31 b guides the sheet S to the fixed tray 23a if the fixed tray 23 a of the discharge section 23 is selected as thedischarge destination of the sheet S in the non-sorting mode.

The third conveyance path 31 c guides the sheet S directly to theprocessing section 22 if the movable tray 23 b of the discharge section23 is selected as the discharge destination of the sheet S in thenon-sorting mode. The third conveyance path 31 c may enable the sheet Sto pass through the standby section 21 without retaining the sheet S inthe standby section 21, when guiding the sheet S directly to theprocessing section 22.

The inlet roller mechanism 32 of the conveyance section 24 includes afirst inlet roller 32 a and a second inlet roller 32 b. The first inletroller 32 a and the second inlet roller 32 b are opposed to each otherin a radial direction thereof with rotation axes parallel to each other.The first inlet roller 32 a is a driven roller disposed on the uppersurface side of the conveyance path 31. The second inlet roller 32 b isa driving roller arranged on the lower surface side of the conveyancepath 31. The first inlet roller 32 a is driven to rotate by a rotationaldriving force transmitted from the second inlet roller 32 b directly orvia the sheet S. The first inlet roller 32 a and the second inlet roller32 b sandwich the sheet S from both sides in the thickness direction ofthe sheet S at a nip therebetween. The first inlet roller 32 a and thesecond inlet roller 32 b convey the sheet S that is sandwiched at thenip to the downstream side in the sheet conveyance direction.

The outlet roller mechanism 33 of the conveyance section 24 comprises afirst outlet roller 33 a and a second outlet roller 33 b. The firstoutlet roller 33 a and the second outlet roller 33 b are opposed to eachother in the radial direction thereof with rotation axes parallel toeach other. The first outlet roller 33 a is a driven roller disposed onthe upper surface side of the first conveyance path 31 a. The secondoutlet roller 33 b is a driving roller disposed on the lower surfaceside of the first conveyance path 31 a. The first outlet roller 33 a isdriven to rotate by a rotational driving force transmitted from thesecond outlet roller 33 b directly or via the sheet S. The first outletroller 33 a and the second outlet roller 33 b sandwich the sheet S fromboth sides in the thickness direction of the sheet S at a niptherebetween. The first outlet roller 33 a and the second outlet roller33 b convey the sheet S that is sandwiched at the nip to the downstreamside in the sheet conveyance direction.

The standby section 21 includes a standby tray 41, an assist guide 43,and a paddle section 45. The sheet conveyance direction in the standbysection 21 is indicated by a first arrow D1 shown in FIG. 3. Thedirection indicated by the first arrow D1 is an approach direction ofthe sheet S from the first outlet roller 33 a and the second outletroller 33 b to the standby tray 41.

The upstream end in the sheet conveyance direction of the standby tray41 is arranged adjacently to the first outlet roller 33 a and the secondoutlet roller 33 b. The upstream end of the standby tray 41 is arrangedbelow the sheet discharge port 31 e of the conveyance path 31 in thevertical direction. The standby tray 41 is tilted with respect to thehorizontal direction in such a manner that the downstream side graduallyrises vertically upwards with respect to the upstream side as itproceeds from the upstream side to the downstream side in the sheetconveyance direction. A plurality of sheets S is stacked in thethickness direction on the standby tray 13 and stands by while theprocessing section 22 performs the post-processing on the former sheetS.

The standby tray 41 includes a pair of tray members moving in mutuallyopposite directions in a sheet width direction. The sheet widthdirection is parallel to a plans of the sheet S and perpendicular to thesheet conveyance direction. The pair of the tray members moves towardseach other to support the sheet S if the sheet S stands by on thestandby tray 41. In a case of moving the sheet S from the standby tray41 to the processing section 22, the pair of the tray members moves awayfrom each other to release the support of the sheet S. The pair of thetray members drops the sheet S towards the processing section 22 bymoving away from each other and then releasing the support of the sheetS.

The assist guide 43 is arranged above the standby tray 41 in thevertical direction. For example, the length of the assist guide 43 inthe sheet conveyance direction is the same as that of the standby tray41 in tire sheet conveyance direction. The assist guide 43 presses thesheet S towards the processing section 22 in a case of moving the sheetS from the standby tray 41 to the processing section 22. The assistguide 43 has a swing shaft parallel to the sheet width direction at thedownstream end of the sheet conveyance direction. The upstream end ofthe assist guide 43 in the sheet conveyance direction is swung aroundthe swing shaft. The upstream end of the assist guide 43 in the sheetconveyance direction is swung downwards to about against the sheet S ina case of pressing the sheet S towards the processing section 22.

The paddle section 45 is arranged between the upstream end of thestandby tray 41 and the processing section 22. The paddle section 45includes a rotation axis parallel to the sheet width direction and apaddle 45 a rotating around the rotation axis. For example, the paddle45 a is made of an elastic material such as rubber. The paddle section45 a rotates around the rotation axis while contacting with, the sheet Swhen the sheet S is moved from the standby tray 41 to the processingsection 22. For example, the paddle section 45 a rotates in acounterclockwise direction shown in FIG. 3. The paddle 45 a moves thesheet S falling down to the processing section 22 from the standby tray41 towards the upstream end of the processing section 22 in the sheetconveyance direction. The paddle 45 a enables the sheet S to contactwith the upstream end of the processing section 22 in the sheetconveyance direction to align the position of the rear end of the sheetS in the sheet conveyance direction. The paddle 45 a aligns the positionof the sheet S in the sheet conveyance direction in the processingsection 22 (that is, the paddle 45 a causes the position of the sheet Sto be in a longitudinal alignment).

The paddle section 45, together with a conveyance roller 59 and a rearend stopper 54 of the processing section 22 described later, constitutesa longitudinal alignment device which performs the longitudinalalignment of the sheet S in the sheet conveyance direction.

The processing section 22 includes a processing tray 51, a pair ofhorizontal alignment plates 52, the rear end stopper 54, a stapler 55,an ejector 56, a thruster 56 a, a bundle claw 57, a bundle claw belt 58,and the conveyance roller 59. The sheet conveyance direction in theprocessing section 22 is indicated by a second arrow D2 shown in FIG. 3.The direction of the second arrow D2 is a discharge direction of thesheet S from the processing tray 51.

The processing tray 51 is arranged below the standby tray 41 in thevertical direction. The processing tray 51 is tilted with respect to ahorizontal direction in such a manner that the downstream side thereofgradually rises upwards in the vertical direction with respect to theupstream side thereof as it goes from the upstream side to thedownstream side in the sheet conveyance direction. For example, theprocessing tray 51 is arranged in parallel with the standby tray 41. Theprocessing tray 51 includes a conveyance surface 51 a on which the sheetS is placed. The conveyance surface 51 a supports the sheet S.

The pair of the horizontal alignment plates 52 is arranged away fromeach other in the sheet width direction at the conveyance surface 51 aof the processing tray 51. The pair of the horizontal alignment plates52 moves in mutually opposite directions in the sheet width direction.The pair of the horizontal alignment plates 52 aligns the positions ofboth ends in the sheet width direction of the sheet S by moving towardseach other and sandwiching the sheet S from both sides in the sheetwidth direction. The pair of the horizontal alignment plates 52 alignsthe position of the sheet S in the sheet width direction (i.e., in ahorizontal alignment). The pair of the horizontal alignment plates 52moves away from each other at the time of releasing the clamping of thesheet S.

The rear end stopper 54 is arranged at the end in the sheet conveyancedirection of the processing tray 51. For example, the shape of the rearend stopper 54 is a hook shape. The rear end stopper 54 supports therear end in the sheet conveyance direction of the sheet S placed on theprocessing tray 51.

The stapler 55 is a binding section which executes the binding processwith the staple on the sheet bundle SS formed by aligning a plurality ofthe sheets S. The stapler 55 is arranged at the rear side of theupstream end in the sheet conveyance direction of the processing tray51. A plurality of the sheets S is supported by the rear end stopper 54and the positions of the rear ends thereof are aligned, and then therear ends of the plurality of the sheets are tightened by the stapler 55to be fixed. If the stapling mode is selected, the stapler 55 executesthe stapling process on the sheet bundle SS, which is supported by therear and stopper 54 and of which the rear end thereof is aligned.

The ejector 56 is arranged at the upstream end of the processing tray 51in the sheet conveyance direction. The ejector 56 is arranged so as tooverlap with the rear end stopper 54 if viewed from the sheet widthdirection at a reference position. For example, the shape of the ejector56 is a hook shape. The ejector 56 supports the rear end in the sheetconveyance direction of the sheet bundle SS subjected to the staplingprocess and the sorting process.

The ejector 56 moves to the sheet conveyance direction with respect tothe processing tray 51. For example, the ejector 56 moves from thereference position towards the downstream side in the sheet conveyancedirection by a driving force transmitted from a driving source. Forexample, if the ejector 56 is disconnected from the driving source, theejector 56 moves to the reference position by a returning force towardsthe upstream side in the sheet conveyance direction applied by anelastic member.

The ejector 56 moves from the upstream side to the downstream side inthe sheet conveyance direction while supporting the sheet bundle SS andmoves the sheet bundle SS cowards the downstream side in the sheetconveyance direction. The ejector 56 moves the end of the sheet bundleSS to a position where the sheet bundle SS is delivered to the bundleclaw 57.

The thruster 56 a is arranged along the conveyance surface 51 a. Forexample, the shape of the thruster 56 a is a plate shape. The thruster56 a moves in the sheet conveyance direction together with the elector56. At the reference position, the thruster 56 a is arranged on theupstream side in the sheet conveyance direction with respect to theconveyance roller 59. If moving towards the downstream side in the sheetconveyance direction from the reference position, the tip of thethruster 56 a in the sheet conveyance direction projects towards thedownstream side in the sheet conveyance direction with respect to theconveyance roller 59. The thruster 56 a protrudes towards the downstreamside in the sheet conveyance direction with respect to the conveyanceroller 59 so as to extend the conveyance surface 51 a towards thedownstream side in the sheet conveyance direction. The thruster 56 acontacts with the lower surface of the sheet S protruding towards thedownstream side in the sheet conveyance direction with respect to theconveyance roller 59 to support the sheet S.

The bundle claw 57 is an extruding member (extruder) that extrudes thesheet bundle SS on the processing tray 51 towards the downstream side inthe sheet conveyance direction to move the sheet bundle SS. The bundleclaw 57 is fixed to the bundle claw belt 58. The shape of the bundleclaw 57 may be hook shape, for example. The bundle claw belt 58 is woundaround a pair of a first belt roller 58 a and a second belt roller 58 bwhich are arranged apart from each other in the sheet conveyancedirection of the processing tray 51. The first belt roller 58 a isarranged at the downstream side in the sheet conveyance direction withrespect to the second belt roller 58 b. The first belt roller 58 a is adriving roller and rotationally drives the bundle claw belt 58. Thesecond belt roller 58 b is a driven roller and is driven to rotate by arotational driving force transmitted from the first belt roller 58 a viathe bundle claw belt 58.

The bundle claw 57 moves as the bundle claw belt 58 rotates. The bundleclaw 57 contacts with the rear end in the sheet conveyance direction ofthe sheet bundle SS placed on the processing tray 51 and conveys thesheet bundle SS in such a manner that it extrudes the sheet bundle SStowards the downstream side in the sheet conveyance direction. Thebundle claw 57 stands by at a position in front of the second beltroller 56 b in an opposite direction to the sheet conveyance directionas a home position HP at the lower surface side of the processing tray51. Whether the bundle claw 57 is present at the home position HP isdetected by a sensor.

For example, the bundle claw 57 moves from the home position HP towardsthe second belt roller 58 b at the lower surface side of the processingtray 51 as the bundle claw belt 58 rotates in a forward direction. Theforward rotation of the bundle claw belt 58 is a counterclockwiserotation as shown in FIG. 3. The bundle claw 57 moves along the outerperiphery of the second belt roller 58 b from the lower surface side tothe upper surface side of the processing tray 51. The upper surface sideof the processing tray 51 is the conveyance surface 51 a side. At theupper surface side of the processing tray 51, the bundle claw 57receives the sheet bundle SS from the ejector 56 and moves towards thedownstream side in the sheet conveyance direction. The bundle claw 57moves along the outer periphery of the first belt roller 58 a towardsthe lower surface side of the processing tray 51 while conveying thesheet bundle SS. The bundle claw 57 extrudes the sheet bundle SS towardsthe downstream side to discharge the sheet bundle SS.

For example, the bundle claw 57 moves towards the upstream side in thesheet conveyance direction at the upper surface side of the processingtray 51 as the bundle claw belt 58 rotates reversely after the dischargeof the sheet bundle SS. The bundle claw 57 moves along the outerperiphery of the second belt roller 58 b from the upper surface side tothe lower surface side of the processing tray 51 to return to the homeposition HP.

The bundle claw belt 58, the first belt roller 58 a and the second beltroller 58 b constitute the bundle claw driving mechanism 61 for drivingthe bundle claw 57.

The bundle claw driving mechanism 61 is provided with a bundle clawdrive motor 62. For example, the bundle claw drive motor 62 is a drivingsource for the first belt roller 58 a, the ejector 56, and the thruster56 a. The bundle claw drive motor 62 is always connected to the firstbelt roller 58 a. The bundle claw drive motor 62 is connected to theejector 56 and the thruster 56 a via an electromagnetic clutch 63.

The electromagnetic clutch 63 transmits the driving force of the bundleclaw drive motor 62 to the ejector 56 and the thruster 56 a at the timeof ON (connection). The electromagnetic clutch 63 interrupts thetransmission of the driving force of the bundle claw drive motor 62 tothe ejector 56 and the thruster 56 a at the time of OFF (disconnection).For example, the bundle claw drive motor 62 rotates the bundle claw belt58 counterclockwise or clockwise as shown in FIG. 3 when theelectromagnetic clutch 63 is turned on. The bundle claw drive motor 62moves the ejector 56 and the thruster 56 a towards the downstream sidein the sheet conveyance direction from the reference position when thebundle claw belt 58 is driven to rotate counterclockwise.

The conveyance roller 59 is arranged so as to overlap with the firstbelt roller 58 a if viewed from the sheet width direction. Theconveyance roller 59 aligns the position of the rear end in the sheetconveyance direction of the sheet S placed on the processing tray 51.The conveyance roller 59 functions as a longitudinal alignment rollerfor aligning the position of the sheet S in the sheet conveyancedirection. The conveyance roller 59, the paddle section 45 and the rearend stopper 54 constitute a longitudinal aligning device forlongitudinally aligning the sheet S. For example, the conveyance roller59 rotates clockwise as shown in FIG. 3 to convey the sheet S placed onthe processing tray 51 towards the rear end stopper 54. The conveyanceroller 59 cooperates with the paddle section 45 to perform thelongitudinal alignment on the sheet S by enabling the rear end of thesheet S to abut against the rear end stopper 54.

The conveyance roller 59 conveys the sheet S placed on the processingtray 51 towards the movable tray 23 b of the discharge section 23. Forexample, the conveyance roller 59 rotates counterclockwise as shown inFIG. 3 to convey the sheet S towards the downstream side in the sheetconveyance direction. The conveyance roller 59 applies a driving forceto the sheet S placed on the processing tray 51 by contacting with thesheet S at the lower surface side of the sheet S. The conveyance roller59 sandwiches the sheet S at a nip between the conveyance roller 59 anda pinch roller 72 which is moved to a rotational position by the pinchroller driving mechanism 71 to apply the driving force to the sheet S.

The pinch roller driving mechanism 71 includes a support arm 73 thatsupports the pinch roller 72 and a solenoid 74 that drives the supportarm 73.

The pinch roller 72 is a driven roller having no driving source. Thepinch roller 72 moves between a standby position above the standby tray41 in the vertical direction and a rotational position close to theconveyance roller 59 below the standby position in the verticaldirection. The pinch roller 72 at the rotational position and theconveyance roller 59 are opposed to each other in a radial directionwith their rotation axes parallel to each other. The pinch roller 72 atthe rotational position sandwiches the sheet S with the conveyanceroller 59 and is driven to rotate by the rotational driving force of theconveyance roller 59 transmitted via the sheet S.

The support arm 73 supports the pinch roller 72 at the tip thereof. Thesupport arm 73 has a swing shaft parallel to the sheet width directionat a base end thereof. The support arm 73 rotates around the swing shaftand swings the pinch roller 72 between the standby position and therotational position.

The solenoid 74 is connected to the base end of the support arm 73. Forexample, the solenoid 74 is a latching type solenoid. If a plungerprotrudes, the solenoid 74 swings the pinch roller 72 upwards via thesupport arm 73. The solenoid 74 moves the pinch roller 72 to the standbyposition away from the conveyance roller 59 as the plunger protrudes. Ifthe plunger sinks, the solenoid 74 swings the pinch roller 72 downwardsvia the support arm 73. The solenoid 74 moves the pinch roller 72 to therotational position close to the conveyance roller 59 as the plungersinks.

When discharging the sheet S or the sheet bundle SS from the processingtray 51 to the movable tray 23 b, the post-processing controller 25switches the process according to a state quantity of the sheet S or thesheet bundle SS. For example, the state quantity of the sheet S or thesheet bundle SS refers to the size (shoot size) of the sheet S, thenumber of sheets (number of stapled sheets) of the sheet bundle SS, thetype of the sheet S, and the like.

For example, as shown in the following Table 1, the post-processingcontroller 25 switches the discharge process according to the sheet sizeand the number of stapled sheets. The post-processing controller 25acquires information relating to the selection of discharge process inresponse to an operation by the user on the control panel 11.

TABLE 1 NUMBER OF STAPLED SHEETS LESS THAN PREDETERMINED PREDETERMINEDNUMBER OF SHEETS SHEET SIZE NUMBER OF SHEETS OR MORE LESS THAN FIRSTDISCHARGE FIRST DISCHARGE PREDETERMINED PROCESS PROCESS THRESHOLD(DISCHARGE BY (DISCHARGE BY VALUE BUNDLE CLAW) BUNDLE CLAW)PREDETERMINED SECOND DISCHARGE THIRD DISCHARGE THRESHOLD PROCESS PROCESSVALUE (DISCHARGE BY (DISCHARGE BY OR MORE PINCH ROLLER) BUNDLE CLAW +ASSISTANCE OF PINCH ROLLER)

If the sheet size is smaller than a predetermined threshold value, thepost-processing controller 25 executes a first discharge process. Thefirst discharge process is an extrusion discharge process for conveyingthe sheet S or the sheet bundle SS only by the bundle claw 57. Forexample, a size less than the predetermined threshold value includes anA4 size or a letter size in the regular size. In the first dischargeprocess, the pinch roller 72 is stopped at the standby position and thesheet S or the sheet bundle SS is discharged by the bundle claw 57. Thepost-processing controller 25 is connected with the electromagneticclutch 63 to start driving the bundle claw drive motor 62 after thelongitudinal alignment and the lateral alignment of the sheet S or thebinding process of the sheet bundle SS is completed. The bundle clawdrive motor 62 moves the ejector 56 and the thruster 56 a from thereference position towards the downstream side in the sheet conveyancedirection. The ejector 56 extrudes the sheet S or the sheet bundle SStowards the downstream side in the sheet conveyance direction. The tipof the thruster 56 a in the sheet conveyance direction protrudes towardsthe downstream side in the sheet conveyance direction with respect tothe conveyance roller 59. The bundle claw drive motor 62 drives thebundle claw belt 58 to rotate and moves the bundle claw 57 from the homeposition HP towards the downstream side in the sheet conveyancedirection at the upper surface side of the processing tray 51. Thebundle claw 57 receives the sheet S or the sheet bundle SS from theejector 56 at the upper surface side of the processing tray 51 andextrudes the sheet S or the sheet bundle SS towards the movable tray 23b on the downstream side in the sheet conveyance direction. Thepost-processing controller 25 disconnects the electromagnet clutch 63and returns the ejector 56 and the thruster 56 a to the referencepositions before the conveyance of the sheet S or the sheet bundle SS iscompleted. The post-processing controller 25 rotationally drives thebundle claw belt 58 in a reverse direction after the conveyance of thesheet S or the sheet bundle SS is completed, and then returns the bundleclaw 57 to the home position HP thereof. For example, the reversedirection is the clockwise direction in FIG. 3.

If the sheet size is equal to or larger than the predetermined thresholdvalue and the number of stapled sheets is less than the predeterminedthreshold value, the post-processing controller 25 executes a seconddischarge process. The second discharge process is a roller dischargeprocess for conveying the sheet S or the sheet bundle SS only by theconveyance roller 59 and the pinch roller 72. For example, a size equalto or larger than the predetermined threshold value includes an A3 size,a leisure size, or the like in a regular size. In the second dischargeprocess, the bundle claw 57 is stopped at the home position HP and thesheet S or the sheet bundle SS is discharged by the conveyance roller 59and the pinch roller 72. The post-processing controller 25 moves thepinch roller 72 from the standby position to the rotational positionafter the longitudinal alignment and the lateral alignment of the sheetS or the binding process of the sheet bundle SS is completed. Thepost-processing controller 25 is connected with the electromagneticclutch 63 to start conveying the sheet S or the sheet bundle SS. Thepost-processing controller 25 starts driving the bundle claw drive motor62 to move the ejector 56 and the thruster 56 a from the referenceposition to the downstream side in the sheet conveyance direction. Theejector 56 extrudes the sheet S or the sheet bundle SS to the downstreamside in the sheet conveyance direction. The tip of the thruster 56 a inthe sheet conveyance direction protrudes towards the downstream side inthe sheet conveyance direction with respect to the conveyance roller 59.The conveyance roller 59 and the pinch roller 72, together with theejector 56, convey the sheet S or the sheet bundle SS to the movabletray 23 b on the downstream side in the sheet conveyance direction. Thepost-processing controller 25 is disconnected from the electromagneticclutch 63 and returns the ejector 56 and the thruster 56 a to thereference position before the conveyance of the sheet S or the sheetbundle SS is completed.

If the sheet size is equal to or larger than the predetermined thresholdvalue and the number of stapled sheets is equal to or larger than thepredetermined threshold value, the post-processing controller 25executes a third discharge process. The third discharge process is acombined discharge process for discharging the sheet S or the sheetbundle SS by the bundle claw 57, the conveyance roller 59 and the pinchroller 72. In the third discharge process, the conveyance of the sheet Sor the sheet bundle SS by the bundle claw 57 is assisted by theconveyance roller 59 and the pinch roller 72.

Hereinafter, with reference to FIG. 4, FIG. 5, FIG. 6, FIG. 7, FIG. 8,FIG. 9, FIG. 10, FIG. 11, FIG. 12, and FIG. 13, the flow of the thirddischarge process in the sheet processing apparatus 3 of the embodimentis described.

FIG. 4 is a first flowchart for depicting the flow of the thirddischarge process in the sheet processing apparatus 3 according to theembodiment. FIG. 5 is a second flowchart for depicting the flow of thethird discharge process in the sheet processing apparatus 3 according tothe embodiment. FIG. 6 is a side view illustrating a first operationstate in the third discharge process of the sheet processing apparatus 3according to the embodiment. FIG. 7 is a side view illustrating a secondoperation state in the third discharge process of the sheet processingapparatus 3 according no the embodiment. FIG. 8 is a side viewillustrating a third operation state in the third discharge process ofthe sheet processing apparatus 3 according to the embodiment. FIG. 9 isa side view illustrating a fourth operation state in the third dischargeprocess of the sheet processing apparatus 3 according to the embodiment.FIG. 10 is a side view illustrating a fifth operation state in the thirddischarge process of the sheet processing apparatus 3 according to theembodiment. FIG. 11 is a side view illustrating a sixth operation statein the third discharge process of the sheet processing apparatus 3according to the embodiment. FIG. 12 is a side view illustrating aseventh operation state in the third discharge process of the sheetprocessing apparatus 3 according to the embodiment. FIG. 13 is a sideview illustrating an eighth operation state in the third dischargeprocess of the sheet processing apparatus 3 according to the embodiment.

First, the post-processing controller 25 moves the movable tray 23 b tothe standby position (ACT 01). The post-processing controller 25 raisesthe movable tray 23 b upwards in the vertical direction to make analtitude difference between the movable tray 23 b and the processingtray 51 less than a predetermined difference. The standby position ofthe movable tray 23 b is a position below a protrusion position of thethruster 56 a in the vertical direction, which does not interfere withthe thruster 56 a.

Next, the post-processing controller 25 energizes the solenoid 74 tolower the pinch roller 72 from the standby position to the rotationalposition (ACT 02). As in the first operation state shown in FIG. 6, thepost-processing controller 25 sandwiches the sheet bundle SS between thepinch roller 72 and the conveyance roller 59.

The post-processing controller 25 energizes the electromagnetic clutch63 to connect the bundle claw drive motor 62 in a stopped state with theejector 56 (ACT 03).

The post-processing controller 25 starts driving the conveyance roller59 to convey the sheet bundle SS to the downstream side in the sheetconveyance direction (ACT 04). Along with the start of driving theconveyance roller 59, the post-processing controller 25 starts loweringthe movable tray 23 b downwards in the vertical direction.

The post-processing controller 25 waits for a predetermined period oftime while continuing to drive the conveyance roller 59 (ACT 05). Forexample, the predetermined period of time is several tens ofmilliseconds or the like, and is taken to eliminate deflection of thesheet bundle SS.

The post-processing controller 25 starts driving the bundle claw drivemotor 62 (ACT 06). As in the second operation state shown in FIG. 7, thepost-processing controller 25 moves the elector 56 and the thruster 56 afrom the reference position towards the downstream side in the sheetconveyance direction. If the ejector 56 contacts with the rear end ofthe sheet bundle SS in the sheet conveyance direction, the ejector 56extrudes the sheet bundle SS towards the downstream side in the sheetconveyance direction. The tip of the thruster 56 a in the sheetconveyance direction protrudes towards the downstream side in the sheetconveyance direction with respect to the conveyance roller 59. Thepost-processing controller 25 drives the bundle claw belt 58 to rotateand moves the bundle claw 57 from the home position HP to the downstreamside in the sheet conveyance direction on the upper surface side of theprocessing tray 51.

The post-processing controller 25 energizes the solenoid 74 to apply adriving force towards the rotational position to the pinch roller 72(ACT 07). As in the third operation state shown in FIG. 8, thepost-processing controller 25 drives the pinch roller 72 in a descendingdirection at a timing when the bundle claw 57 receives the sheet bundleSS from the ejector 56. The post-processing controller 25 presses thesheet bundle SS towards the conveyance roller 59 and the conveyancesurface 51 a by the pinch roller 72 driven in the descending direction.This prevents the pinch roller 72 from rising and prevents the sheetbundle SS from bending.

The post-processing controller 25 determines whether or not an amount ofdriving by the bundle claw drive motor 62 reaches a first predeterminedamount (ACT 08). For example, the amount of driving by the bundle clawdrive motor 62 is the number of steps.

If the determination result is “No” (No in ACT 08), the post-processingcontroller 25 repeatedly executes the determination process in ACT 08.

On the other hand, if the determination result is “Yes” (Yes in ACT 08),the post-processing controller 25 proceeds to the process in ACT 09.

The post-processing controller 25 stops energizing the electromagneticclutch 63 and disconnects the bundle claw drive motor 62 from theejector 56 (ACT 09). As in the fourth operation state shown in FIG. 9,the post-processing controller 25 moves the ejector 56 and the thruster56 a to the reference position by the return force towards the upstreamside in the sheet conveyance direction. The post-processing controller25 lowers the movable tray 23 b downwards in the vertical direction to aposition at least below a movement locus of the thruster 56 a.

The post-processing controller 25 determines whether or not the amountof driving by the bundle claw drive motor 62 reaches a secondpredetermined amount which is larger than the first predetermined amount(ACT 10).

If the result of the determination is “No” (No in ACT 10), thepost-processing controller 25 repeatedly executes the determinationprocess in (ACT 10).

On the other hand, if the determination result is “Yes” (Yes in ACT 10),the post-processing controller 25 proceeds to the process in ACT 11.

The post-processing controller 25 energizes the solenoid 74 to raise thepinch roller 72 from the rotational position to the standby position(ACT 11). As in a process from the fifth operation state shown in FIG.10 to the sixth operation state shown in FIG. 11, the post-processingcontroller 25 avoids interference between the bundle claw 57 moving inthe sheet conveyance direction and the pinch roller driving mechanism71.

The post-processing controller 25 determines whether or not the amountof driving by the bundle claw drive motor 62 reaches a predeterminedtarget amount of driving and the driving by the bundle claw drive motor62 is completed (ACT 12).

If the result of this determination is “No” (No in ACT 12), thepost-processing controller 25 repeatedly executes the determinationprocessing in ACT 12.

On the other hand, if the determination result is “Yes” (Yes in ACT 12),the post-processing controller 25 proceeds to the process in ACT 13. Asin the seventh operation state shown in FIG. 12, the post-processingcontroller 25 determines that the discharge of the sheet bundle SS fromthe processing tray 51 to the movable tray 23 b is completed, and thenproceeds to the process in ACT 13.

The post-processing controller 25 starts driving the bundle claw drivemotor 62 so as to drive the bundle claw belt 58 to rotate in the reversedirection to return the bundle claw 57 to the home position HP (ACT 13).For example, the reverse direction is the clockwise direction shown inFIG. 12. The post-processing controller 25 moves the bundle claw 57towards the upstream side in the sheet conveyance direction at the uppersurface side of the processing tray 51. The post-processing controller25 moves the bundle claw 57 along the outer periphery of the second beltroller 58 b from the upper surface side of the processing tray 51 to thelower surface side thereof. The post-processing controller 25 moves thebundle claw 57 towards the home position HP from the second belt roller58 b at the lower surface side of the processing tray 51.

The post-processing controller 25 determines whether or not the amountof driving of the conveyance roller 59 reaches a predetermined targetamount of driving and the driving of the conveyance roller 59 iscompleted (ACT 14).

If the determination result is “No” (No in ACT 14), the post-processingcontroller 25 repeatedly executes the determination processing in ACT14.

On the other hand, if the determination result is “Yes” (Yes in ACT 14),the post-processing controller 25 proceeds to the process in ACT 15.

The post-processing controller 25 determines whether or not the bundleclaw 57 reaches the home position HP and the driving by the bundle clawdrive motor 62 is completed (ACT 15). As in the eighth operation stateshown in FIG. 13, the post-processing controller 25 determines whetheror not a sensor detects that the bundle claw 57 is present at the homeposition HP.

If the determination result is “No” (No in ACT 15), the post-processingcontroller 25 repeatedly executes the determination processing in ACT15.

On the other hand, if the determination result is “Yes” (Yes in ACT 15),the post-processing controller 25 terminates the process.

Since the sheet processing apparatus 3 of the embodiment described abovehas the post-processing controller 25 for controlling sheet conveyanceby the conveyance roller 59, the pinch roller 72, and the bundle claw57, the stability of conveyance can be improved. With thepost-processing controller 25 for conveying the sheet by the conveyanceroller 59 and the pinch roller 72 prior to sheet conveyance by thebundle claw 57, bending of the sheet S can be prevented. With thepost-processing controller 25 for moving the pinch roller 72 to thestandby position prior to sheet conveyance by the bundle claw 57, theinterference between the bundle claw 57 and the pinch roller 72 can beprevented. With the post-processing controller 25 for conveying thesheet with the bundle claw 57 after the sheet is conveyed by theconveyance roller 59 and the pinch roller 72, the sheet S can beaccurately conveyed.

With the post-processing controller 25 for applying the force towardsthe rotational position to the pinch roller 72 when the sheet isconveyed by the conveyance roller 59 and the pinch roller 72, bending ofthe sheet S caused by the ascent of the pinch roller 72 can beprevented. With the post-processing controller 25 which applies theforce towards the rotational position to the pinch roller 72, the pinchroller 72 can press the sheet S towards the conveyance roller 59,thereby preventing the bending of the sheet.

With the post-processing controller 25 for switching the selectionbetween the roller discharge process and the combined discharge process,bending of the sheet S can be prevented and the stability of dischargeof the sheet S can be improved. With the post-processing controller 25for switching the selection between roller discharge process andcombined discharge process according to the number of sheets S,conveyance failure due to an increase in the number of sheets S can beprevented. With the post-processing controller 25 which carries outcombined discharge process depending or the number of sheets S, it ispossible to accurately convey the sheet S by the bundle claw 57, theconveyance roller 59 and the pinch roller 72. Even if there are a largenumber of sheets S, the bundle claw 57 can accurately transmit thedriving force in the sheet conveyance direction, and the stability ofthe conveyance can be improved.

With the post-processing controller 25 for switching the selectionbetween the roller discharge process or the combined discharge processand the extrusion discharge process, bending of the sheet S can beprevented and the stability of discharge of the sheet S can be improved.With the post-processing controller 25 which switches between the rollerdischarge process or the combined discharge process and the extrusiondischarge process depending on the size of the sheet S, it is possibleto prevent the sheet S from bending caused by an increase in the sheetsize. With the post-processing controller 25 which performs the rollerdischarge process or the combined discharge process depending on thesize of the sheet S, the bending of the sheet S can be prevented by theconveyance roller 59 and the pinch roller 72. With the conveyance roller59 and the pinch roller 72, the bending of the sheet S can be prevented,and the conveyance failure can also be prevented even if the size of thesheet S is large or the rigidity of the sheet S is low.

With the post-processing controller 25 which drives the conveyanceroller 59 to rotate in the sheet conveyance direction prior to sheetconveyance by the bundle claw 57, the bending of the sheet S can beprevented. Even if the sheet S on the processing tray 51 bends, theconveyance roller 59 can reduce a bending amount by being driven torotate in the sheet conveyance direction.

Modifications of the embodiment are described below.

In the above-described embodiment, the post-processing controller 25switches the selection between the first discharge process and thesecond discharge process or the third discharge process depending on thesheet size, but the present invention is not limited thereto.

The post-processing controller 25 may perform the second dischargeprocess or the third discharge process without performing the firstdischarge process regardless of the sheet size.

In the above-described embodiment, the post-processing controller 25 maychange at least one of tine conveyance speed of the conveyance roller 59and the conveyance speed of the bundle claw 57. The post-processingcontroller 25 may change the conveyance speed of at least one of theconveyance roller 59 and the bundle claw 57 according to the statequantity of the sheet S or the sheet bundle SS.

In the embodiment described above, all or a part of the functions of thesheet processing apparatus 3 may be realized by hardware. The hardwareis, for example, a LSI (Large Scale Integration), an ASIC (ApplicationSpecific Integrated Circuit), a PLD (Programmable Logic Device), a FPGA(Field Programmable Gate Array), or the like.

The programs executed by each CPU of the sheet processing apparatus 3may be recorded on a computer-readable recording medium. The recordingmedium is, for example, a portable medium such as a flexible dish, amagneto-optical disk, a ROM, a CD-ROM, or the like, or a storage devicesuch as a hard disk built in a computer system. The programs may betransmitted via an electric communication line.

According to at least one embodiment described above, with thepost-processing controller 25 for controlling sheet conveyance by theconveyance roller 59, the pinch roller 72, and the bundle claw 57, thestability of conveyance can be improved. With the post-processingcontroller 25 for conveying the sheet by the conveyance roller 59 andthe pinch, roller 72 prior to sheet conveyance by the bundle claw 57,bending of the sheet S can be prevented. With the post-processingcontroller 25 for moving the pinch roller 72 to the standby positionprior to sheet conveyance by the bundle claw 57, the interferencebetween the bundle claw 57 and the pinch roller 72 can be prevented.With the post-processing controller 25 for conveying the sheet with thebundle claw 57 after the sheet is conveyed by the conveyance roller 59and the pinch roller 72, the sheet S can be accurately conveyed.

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the invention. Indeed, the novel embodiments described hereinmay be embodied in a variety of other forms; furthermore, variousomissions, substitutions and changes in the form of the embodimentsdescribed herein may be made without departing from the spirit of theinvention. The accompanying claims and their equivalents are intended tocover such forms or modifications as would fall within the scope andspirit of the invention.

What is claimed is:
 1. A sheet processing apparatus, comprising: aprocessing tray configured to stack a sheet; a conveyance roller,arranged on a downstream side in a sheet conveyance direction withrespect to the processing tray, configured to convey the sheet towardsthe downstream side in the sheet conveyance direction; a pinch rollerconfigured to move between a first position distal from the conveyanceroller and a second position proximate to the conveyance roller, and tosandwich the sheet with the conveyance roller at the second positionwhen the sheet is conveyed by the conveyance roller; an extruderconfigured to extrude an end of an upstream sheet in the sheetconveyance direction from an upstream side towards the downstream sidein the sheet conveyance direction to convey the sheet placed on theprocessing tray; and a controller configured to control the conveyanceroller, the pinch roller and the extruder to move the pinch roller tothe second position when the sheet placed on the processing tray isconveyed to the downstream side in the sheet conveyance direction, movethe pinch roller to the first position from the second position afterthe sheet is conveyed by the pinch roller and the conveyance roller, andthen convey the sheet with the extruder.
 2. The sheet processingapparatus according to claim 1, wherein the controller is configured toapply a force towards the second position to the pinch roller when thesheet is conveyed by the pinch roller and the conveyance roller.
 3. Thesheet processing apparatus according to claim 1, wherein the controlleris configured to switch a selection between a roller discharge processfor conveying the sheet only with the pinch roller and the conveyanceroller and a combined discharge process for conveying the sheet with thepinch roller, the conveyance roller and the extruder, and the controlleris configured to switch the selection based on whether a number ofsheets is less than a predetermined value.
 4. The sheet processingapparatus according to claim 2, wherein the controller is configured toswitch a selection between a roller discharge process for conveying thesheet only with the pinch roller and the conveyance roller and acombined discharge process for conveying the sheet with the pinchroller, the conveyance roller and the extruder, and the controller isconfigured to switch the selection based on whether a number of sheetsis less than a predetermined value.
 5. The sheet processing apparatusaccording to claim 3, wherein the controller is configured to switch aselection between the roller discharge process or the combined dischargeprocess and an extrusion discharge process for conveying the sheet onlyby the extruder, based on whether a sheet size is less than a thresholdvalue.
 6. The sheet processing apparatus according to claim 1, whereinthe controller is configured to drive the conveyance roller to rotate inthe sheet conveyance direction prior to conveyance of the sheet by theextruder.
 7. The sheet processing apparatus according to claim 2,wherein the controller is configured to drive the conveyance roller torotate in the sheet conveyance direction prior to conveyance of thesheet by the extruder.
 8. The sheet processing apparatus according toclaim 1, wherein the conveyance roller is configured to convey the sheetin the conveyance direction along a conveyance path, wherein theconveyance path includes a first conveyance path, a second conveyancepath, and a third conveyance path, the first and second conveyance pathsbeing bifurcated from the first conveyance path.
 9. The sheet processingapparatus according to claim 7, wherein the first conveyance path isarranged to guide the sheet to a standby section, the second conveyancepath is configured to guide the sheet to a discharger, and the thirdconveyance oath is arranged to guide the sheet to the processing tray.10. The sheet processing apparatus according to claim 1, wherein thefirst position is a standby position and the second position is arotational position.
 11. A sheet processing method, comprising:arranging a conveyance roller on a downstream side in a sheet conveyancedirection with respect to a processing tray in which a sheet is stacked,causing the conveyance roller to convey the sheet towards the downstreamside in the sheet conveyance direction; providing a pinch roller to movebetween a first position distal from the conveyance roller and a secondposition proximate to the conveyance roller, and to sandwich the sheetwith the conveyance roller at the second posit ion when the sheet isconveyed by the conveyance roller; causing an extruder to extrude an endof an upstream sheet in the sheet conveyance direction from an upstreamside towards the downstream side in the sheet conveyance direction toconvey the sheet placed on the processing tray; and controlling, by acontroller, the conveyance roller, the pinch roller and the extruder tomove the pinch roller to the second position when the sheet placed onthe processing tray is conveyed to the downstream side in the sheetconveyance direction, move the pinch roller to the first position fromthe second position after the sheet is conveyed by the pinch roller andthe conveyance roller, and then convey the sheet with the extruder. 12.The sheet processing method according to claim 11, further comprising:applying a force towards the second position to the pinch roller whenthe sheet is conveyed by the pinch roller and the conveyance roller. 13.The sheet processing method according to claim 11, further comprising:switching a selection between a roller discharge process for conveyingthe sheet only with the pinch roller and the conveyance roller and acombined discharge process for conveying the sheet with the pinchroller, the conveyance roller and the extruder, wherein the switching isperformed based on whether a number of sheets is less than apredetermined value.
 14. The sheet processing method according to claim12, further comprising: switching a selection between a roller dischargeprocess for conveying the sheet only with the pinch roller and theconveyance roller and a combined discharge process for conveying thesheet with the pinch roller, the conveyance roller and the extruder,wherein the switching is performed based on whether a number of sheetsis less than a predetermined value.
 15. The sheet processing methodaccording to claim 13, further comprising: switching a selection betweenthe roller discharge process or the combined discharge process and anextrusion discharge process for conveying the sheet only by theextruder, based on whether a sheet size is less than a threshold value.16. The sheet processing method according to claim 11, furthercomprising: driving the conveyance roller to rotate in the sheetconveyance direction prior to conveyance of the sheet by the extruder.17. The sheet processing method according to claim 12, furthercomprising: driving the conveyance roller to rotate in the sheetconveyance direction prior to conveyance of the sheet by the extruder.18. The sheet processing method according to claim 11, furthercomprising: conveying, by the conveyance roller, the sheet in theconveyance direction along a conveyance path, wherein the conveyancepath includes a first conveyance path, a second conveyance path, and athird conveyance path, the first and second conveyance paths beingbifurcated from the first conveyance path.